In a typical edge-emitting semiconductor laser diode, an active layer is formed parallel to a p-n junction in a semiconductor wafer, and two cleaved facets of the wafer perpendicular to the active layer function as mirror surfaces to form the laser resonator. To produce a laser beam perpendicular to the semiconductor wafer, special structures (such as 45-degree mirrors or diffraction gratings) must be formed on a surface of the wafer to re-direct the output of the laser resonator in the desired direction.
In a typical surface-emitting semiconductor laser diode, both surfaces of a semiconductor wafer function as mirror surfaces to form the laser resonator, whereby laser emission occurs in a direction perpendicular to a surface of the wafer. A surface-emitting semiconductor laser diode exemplifying the state of the prior art is described in an article entitled "Room Temperature Pulsed Oscillation of GaAlAs/GaAs Surface Emitting Junction Laser" by Kenichi Iga, et al. which was published in the IEEE Journal of Quantum Electronics, Vol. QE-21, No. 6, June 1985, pages 663-668. In general, the active region of a surface-emitting semiconductor laser diode of the prior art is formed parallel to a p-n junction in the semiconductor wafer. Consequently, in surface-emitting semiconductor laser diodes of the prior art, carrier current cannot be confined to the immediate vicinity of the active region, and a rather high threshold current is therefore required to initiate laser action.